No-tillage with total green manure mulching: A strategy to lower N2O emissions

Green manure application in agricultural soil is known to enhance nitrogen use efficiency and crop yield. However, limited research exists on the potential effects of green manure returning on N2O emissions. This study aims to investigate the effects and underlying mechanisms of N2O emissions in maize fields under different green manure management practices. A field experiment was conducted using common vetch as a green manure crop following the harvest of spring wheat. The study employed a completely randomized block design and examined four treatments: tillage with total green manure incorporation, no-tillage with total green manure mulching (NTG), tillage with green manure root incorporation (T), and no-tillage with aboveground green manure removal (NT). The study explored both non-biological and biological factors affecting nitrogen conversion to elucidate the mechanisms in N2O emissions. N2O emissions were 17.7% lower in TG and NTG compared to T and NT (P < 0.01), with NTG showing a 12.2% reduction compared to TG (P < 0.05). NTG also exhibited the lowest average N2O fluxes at 24.2 μg N m−2 h−1. In terms of non-biological factors, N2O emissions were negatively correlated only with aggregate NH4+-N and NO3--N (P < 0.05). Despite increasing soil mineral nitrogen, NTG had approximately 72.3%− 92.4% of it in the form of aggregate nitrogen. In addition, under NTG, the aggregates have better structure and stability. q-PCR analysis revealed higher nos Z gene abundance in NTG than in other treatments (P < 0.05). Regression analysis showed that N2O emissions were negatively correlated with nos Z's abundance and N2O reductase diversity (P < 0.05). No-tillage with total green manure mulching (NTG) effectively reduced N2O emissions by enhancing mineral nitrogen in soil aggregates and increasing the abundance of the nos Z gene. Our findings offer valuable insights for long-term agricultural management strategies aimed at improving nitrogen retention and mitigating climate change impacts.